How imortant is it to oxidise the surface for silanization? I see some methods that use silnization buffer containing ethanol to activate the APTES and used it directly on PDMS without oxidation.
Oxidation of the PDMS provides the active groups to form covalent bonds with the active sites on the APTES after hydrolysing the ethoxy groups. If there are no sites available on the PDMS to provide the other half of the condensation reaction, then you will not have any of the APTES covalently bonded to the PDMS. While it is possible to have condensation reactions with the methyl side chains, it is not energetically favorable and that surface coating will be sparse and weak.
The ethanol in APTES coating recipes is the solvent. The hydolysis of the ethoxy groups is done by the water. The amount of water will influence the hydrolysis rate and the longevity of the coating solution. Too much water will cause the solution to react too fast and the coatings will be non-uniform. Too little water will cause the coating process to take too long.
Best of luck!
For efficient silanization, there is the need to introduce/activate OH groups on the PDMS surface. This process is usually done in an O2 plasma chamber and takes about 30 sec depending on your system. There are chemical-based processes (using ethanol or hydrogen peroxidase) that also help to activate the OH groups on the PDMS. Well, as you see all these methods use an activation step (whether it's physical or chemical) prior to silanization. I definitely recommend the O2 plasma treatments as its efficient, quick, clean, and reproducible!
Good luck in the lab~
Ron Reiserer Thanks for your explanation. I cannot use plasma to oxidize my PDMS surface as it creates a silica like layer on the PDMS which affects its elasticity. I saw an oxidation method which uses water, H2O2 and HCl in 5:1:1 ratio. But I am not sure whether it will affect the elasticity as well.
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